Calibration of flow sensors for air and gases at SCHMIDT Technology

Calibration of measuring systems provides clarity about their characteristic and allows a more accurate evaluation of the measurement results. It simultaneously achieves referring or basing it on an international system of units. At SCHMIDT Technology, calibrations of flow sensors are carried out at the highest technological level.

Measurements are an important part of industrial quality assurance. However, inherent in each measurement are so-called measuring uncertainties, which may have many causes. To minimize the unavoidably systematic deviations, which to a large extent are also due to the measuring devices themselves, they can be calibrated or recalibrated.

Calibration of a measuring system is by definition "An activity for determining the relationship between the output values of a measuring device … and the associated values of a measuring quantity established standards under specified conditions". The obtained comparative results do not lead to adjustment via an intervention in the device. They are recorded in a measurement log and output in the form of a calibration certificate. This means that calibration leads to detailed knowledge about the characteristics of a measuring system, which increases with increasing number of the calibration points distributed over the characteristic line. Detailed knowledge of the deviation between actual and target values, i.e., output value and correct value of the measuring quantity, increases the measuring certainty.

Calibrations represent snapshots. However, given that measuring systems are subject to effective loads, changes (drift) take place over time that require repeated calibrations. Moreover, information on the performance of a measuring system with time can only be obtained after repeated recalibrations. Only such considerations allow measuring results between two calibrations to be evaluated

The calibration results are documented in measurement logs and output in the form of calibration certificates. They are ultimately the prerequisite of the use of measuring systems in processes subject to quality monitoring, for example according to ISO 9001:2008 or GMP. As part of calibrations, comparability, i.e., basing calibration on a national standard, which embodies the most accurate implementation of the unit of the international system of units (SI) available in a country, is also provided.

Highly advanced wind tunnels

For the adjustment of every SCHMIDT® flow sensor as part of ist manufacture as well as for its calibration, SCHMIDT Technology has highly advanced wind tunnels available. The sensors are measured fully automatically either in the open jet of an atmospheric wind tunnel or in the measuring tube of a pressure wind tunnel. This allows all measuring ranges to be covered, ranging from minute flow velocities, as required in cleanroom applications, to 70 m/s (atmospheric wind tunnel) or even to standardized flow velocities of 200 m/s (pressure wind tunnel of up to 6 bar). In addition, the pressure wind tunnel also allows measurements in inert gases (e.g. argon, CO2, nitrogen, helium …). Thus, no conversion tables involving the resulting uncertainties are required, because actual measuring values are available. This means that adjustment and calibrations can be carried out very close to the operating conditions at the user's.

At the testing and calibration laboratories at SCHMIDT Technology, the high-end technology is also present in the form of a laser Doppler anemometer (LDA) reference unit for the contactless measurement of flow velocities. This technology is used to calibrate the reference units and the flow profiles in the in-house wind tunnels at the highest possible level. Down to the LDA reference units, the SCHMIDT® wind tunnels secure high-end measuring accuracies of the SCHMIDT® flow sensors.